1. Technical Field
The present invention relates to a fiber composite twisted cable and, more specifically, to a twisted cable in which carbon fibers and thermosetting resin as a matrix are combined.
2. Description of the Related Art
Among high-strength low ductility fibers, carbon fibers have characteristics such as light weight, high corrosion resistivity, non-magnetic property, high coefficient of thermal conductivity, ultralow coefficient of thermal expansion, high tensile strength, and high tension modulus. In order to make full use of such characteristics, a fiber composite twisted cable having carbon fibers and thermosetting resin as a matrix combined to each other is known.
The fiber composite twisted cable is manufactured generally by forming strands by twisting bundles of carbon fibers impregnated with thermosetting resin, twisting a plurality of such strands, and then curing the thermosetting resin by heat treatment.
However, there is a problem such that air or residual solvent contained in thermosetting resin remains in the interior of a cable as gaps between a process of impregnating with the thermosetting resin and a process of forming a cable by twisting the plurality of strands, whereby mechanical characteristics such as the tensile strength per cross-sectional area of the cable, which is important characteristics as the fiber composite twisted cable is lowered.
Accordingly, in JP-A-2-127583, a fiber composite twisted cable formed by winding a fiber yarn on an outer periphery of a strand impregnated with thermosetting resin at an angle close to a right angle with respect to the axial direction of the strand in high density, then twisting a plurality of the strands, and then curing the thermosetting resin by heat treatment is proposed.
According to the related art, the fiber bundles are prevented from being unlaid by winding the fiber yarn, and an effect of expelling the air or the residual solvent contained in the interior of the cable is expected by a winding pressure of the fiber yarn. However, when twisting the plurality of strands impregnated with the thermosetting resin, liquid-state thermosetting resin in an uncured state is squeezed out from between the wound fiber yarns, so that the resins from adjacent side strands moisten with respect to each other, and flows into a gap between a core strand and the side strands and stays therein.
Therefore, when the thermosetting resin is cured in a last process, the adjacent strands are adhered and integrated with each other (the core strand and the side strands, and the side strands and the side strands), so that the entire cable becomes cured like a hard rod.
Therefore, bending rigidity of the fiber composite twisted cables in the related art is very high and, consequently, flexibility that the cable should have under normal circumstances by having a twisted wire structure is impaired, and hence a large reel provided with a large-diameter winding barrel is required.
Consequently, when applying the fiber composite twisted cable to a reinforcing member for an overhead transmission line and performing a wiring work in a mountain range for example, problems in transport such that a large vehicle for loading the large reel is required and, road works for moving the large vehicle in turn are required are inevitable.
Furthermore, when winding the fiber composite twisted cable on the reel, partial separation of the thermosetting resin which bonds the strands with respect to each other occurs by bending, so that bonded portions and separated portions exist together between the adjacent strands in the longitudinal direction of the cable. Consequently, there arises a problem such that bending occurs when the cable is withdrawn from the reel when using the cable and hence linearity of the cable is impaired.